In the prior art several types of apparatuses and nozzle heads are used for subjecting a surface of a substrate to successive surface reactions of at least a first precursor and a second precursor according to the principles of atomic layer deposition method (ALD). In ALD applications, a surface of a substrate is typically subjected successively to at least two gaseous precursors. The gaseous precursors effectively react with the substrate surface, resulting in deposition of a single atomic layer. The precursor stages are typically followed or separated by a purge stage that eliminates the excess precursor from the surface of the substrate prior to the separate introduction of the other precursor. Therefore an ALD process requires alternating in sequence the flux of precursors to the surface of the substrate. This repeated sequence of alternating surface reactions and purge stages between is a typical ALD deposition cycle.
The prior art ALD-apparatuses usually comprise a nozzle head having one or more first precursor nozzles for subjecting the surface of the substrate to the first precursor, one or more second precursor nozzles for subjecting the surface of the substrate to the second precursor, and one or more purge gas nozzles arranged between the first and second precursor zones for subjecting the surface of the substrate to a purge gas. The nozzles may be arranged alternatively in succession to the nozzle head: first precursor zone, purge gas zone, second precursor zone, purge gas zone, first precursor zone, purge gas zone, second precursor zone, and so on. Therefore when the nozzle head is moved in relation to the substrate over the surface of the substrate it will produce growth layers according to the principles of ALD method. The nozzle head may also comprise discharge channels arranged between the first and second precursor nozzles or between a first precursor nozzle and a purge gas nozzle or between a second precursor nozzle and a purge gas nozzle. The discharge channels are arranged to exhaust precursor or reaction products and purge gas. Alternatively each of these prior art precursor nozzles and purge gas nozzles may comprise at least one inlet port for supplying the precursor or purge gas and at least one outlet port for exhausting the precursor or purge gas. Thus there is provided suction to each of the nozzles for exhausting the precursor or purge gas.
The nozzle head is usually supported over the surface of the substrate such that there is a predetermined distance between the nozzle head and the surface of the substrate. The substrate is supported to a substrate support such that the mentioned predetermined distance is formed. As only one atomic layer is produced on the surface of the substrate during one ALD-cycle, the nozzle head may comprise several first and second precursor nozzles such that a single scan with the nozzle head over the surface of the substrate forms several atomic layers on the surface of the substrate. The single scan with the nozzle head may be done by moving either the nozzle head or the substrate such that the nozzle head and the substrate are moved in relation to each other. The predetermined distance between the nozzle head and the surface of the substrate is formed as small as possible such that the supply of the precursor materials on the surface of the substrate may be efficiently controlled and precursor materials do not escape to surroundings of the nozzle head and a good coating may be formed on the surface of the substrate. The predetermined distance, or process gap, between the nozzle head and the surface of substrate may be for example 0.3-2 mm, preferably 0.5-1.0 mm.
In typical ALD application the process temperature is over 70° C., usually at least 100° C. or 70 to 150° C. The nozzle head and the other parts of the apparatus undergo thermal expansion due to the elevated process temperature. Usually several materials are used for constructing the ALD apparatus and also different parts of the apparatus may be at different temperature during processing and especially during heating and cooling stages of the apparatus. Therefore, the process gap between the nozzle head and the surface of the substrate may change causing uncontrollable increase or decrease of the process gap. Excessive increase of the process gap leads to operational problems of the apparatus when it is used for coating a substrate. The decrease of the process gap may lead to a contact between nozzle head and the surface of the substrate preventing the operation of the apparatus. When cylindrical substrate support is used the thermal expansion in radial direction may be 1 to 4 mm with a cylinder having radius 0.6-1.2 m. This means that the thermal expansion may be larger than the height of the process gap. When longitudinal substrates are transported through the deposition gap the coating process is kept continuous by connecting successive substrate together with a joint. The joint is provided by attaching the successive substrate superposed. The thickness of the substrate may for example 0.7 mm and in the joint the thickness is at least twice the substrate thickness. Therefore, the joint may not fit through the process gap. In the prior art apparatuses this means process downtime as the nozzle head has to be dismounted.